The invention relates to a control component such as a valve or like member for use in a hydraulic system.
A valve or like member for a hydraulic system is known, comprising an inlet and an outlet for the hydraulic fluid, and a flow passage or throttle bore between the inlet and the outlet, which opens at the end in the direction of flow through the valve, at an outside surface on a valve body portion. Disposed opposite and co-operable with the outside surface of the valve body portion is an inside surface of a sleeve or corresponding member in which the valve body portion is disposed. The inside surface of the sleeve or corresponding member is movable relative to the outside surface of the valve body portion, for flow control purposes. More particularly, with the valve body portion being hollow and screwed into the sleeve or corresponding member, the or each flow passage or throttle bore extends from the hollow interior of the valve body, and is operative to control the flow through the device; a greater or smaller amount of hydraulic fluid can therefore flow through the valve, in dependence on the magnitude of the areas of contact between the co-operable inside and outside surfaces referred to above.
It has been found however that a serious disadvantage of such valves and throttle members for hydraulic fluids is that the lowest constant flow rate is in the region of 0.4 liters per minute. However, in most situations, such a flow rate is too high, and the known valves are therefore unusable in such circumstances.
A further disadvantage arises due to the internal pressure which causes deformation of the valve or throttle sleeve; at pressures at up to around 350 bars, the throttle sleeve sticks or jams, between the flow passages of the valve body portion, over which it becomes enlarged. That consideration means for example that it is only possible under limited conditions to adjust conventional valves under pressure, as the pressure-less edges or lands cause damage to the valve body portion and to the throttle sleeve.